PROJECT SUMMARY/ABSTRACT Obesity arises from an imbalance between the amount of energy stored and consumed and increases the risk of metabolic derangements, imposing significant economic burden to our society. Three types of fat cells -white, brown and beige- are critical for the maintenance of the equilibrium between calories hoarded and those utilized. Augmenting energy dissipation by boosting brown and beige fat thermogenesis has been proposed as a strategy to combat obesity; however, the current arsenal of proteins known to confer thermogenic competency to fat cells remains limited. Our laboratory has discovered that the zinc finger factor ZNF638 is a novel transcriptional regulator of adipocyte function. New work performed in our laboratory has now provided evidence demonstrating that mice lacking ZNF638 in fat tissue have weakened ability to withstand cold temperatures and increased propensity to obesity. Here we propose to assess the physiological role of ZNF638 in adipose tissues and to evaluate the consequences of loss- or gain-of-ZNF638-function on metabolic dysfunction. Furthermore, we plan to determine the molecular mechanisms that regulate ZNF638?s levels and functionality and through which ZNF638 coordinates transcriptional pathways regulating energy balance. At completion, the studies proposed will permit the detailing of ZNF638?s function in fat and the characterization of its upstream regulators, downstream target promoters and transcriptional partnerships, thereby clarifying its mechanism of action. To perform the work proposed we will take advantage of newly generated ZNF638 floxed mice and of molecular and cell biological techniques and reagents utilized in our laboratory over the years. These will be combined with unbiased approaches, as outlined in the aims below. In Aim 1 we will assess the physiological role of ZNF638 in the control of energy expenditure, glucose homeostasis and metabolic dysfunction through the characterization of adipose specific ZNF638 knock-out and overexpressing mice and will establish the genetic requirement and sufficiency of ZNF638 for beige and brown fat functionality; in Aim 2 we will identify the transcriptional and signaling pathways that regulate ZNF638 in adipose tissues and reveal the genome-wide targets of this cofactor in fat using state of the art next generation sequencing technologies. In addition we will define the molecular mechanisms through which ZNF638 regulates transcription in fat cells via the characterization of novel key transcriptional partners that enable ZNF638?s regulation of gene expression. We expect that the studies outlined will shed novel light into the mechanisms regulating energy balance and will ultimately permit the definition of new strategies to modulate energy metabolism with possible impact on the development of anti-obesity therapies.